450 EXC Fork Seal Replacement Tips

Pukmeister

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Changing my leaking fork seal(s) on the KTM this weekend, learned a few things worth passing on:

1) Undoing the fork top nut (rebound adjuster) whilst still in the yokes can prove difficult, with a risk of rounding off the flats on the adjuster housing. They are very tight to undo as fitted to the bike:

My solution was to slacken off both the top and bottom yoke pinch bolts, slide the forks up about 10mm then tighten the lower yokes pinch bolts only. This relieves the grip on the fork tube threads, allowing the fork top nut to undo with only minimal force without risk of wrecking the flats.

2) Undoing the bottom nut (compression adjuster) with forks inverted in the vice using a 19mm double-hex socket (with breaker bar) runs the risk of rounding off the flats due to the stiction of the threads, dirt etc. Be sure to use a single-hex 19mm socket, its still bloody tight but comes undone with force and a whip cracking noise. Mount the front axle through the fork lower and grip in a vice to hold the fork lower slider, you may also need to hold the cartridge with a rag to undo the bottom nut threads and remove the cartridge, otherwise it just keeps spinning.

I'm fitting some aftermarket "all balls" oil seals tomorrow with double lip and dust seals to improve sealing over the stock OEM items. If I experience any other pearls of wisdom on assembly I'll pass the info on.
 
Another tip might be to not undo the top nut at all:D

Remove the old seals with a self tapper, put some oily cling film over the top of the fork leg and slide the new seal down, drive it home evenly using the old one as a drift:thumb
 
Another tip might be to not undo the top nut at all:D

Remove the old seals with a self tapper, put some oily cling film over the top of the fork leg and slide the new seal down, drive it home evenly using the old one as a drift:thumb

Thanks for the advice Tim but mine are USD WP forks, I believe you have no choice but to separate the lower slider from the upper stanchion to remove/replace the seals. I can see how the method you suggest would work for conventional right way up forks though, and would save a lot of hassle.

Did the seals today, fully stripped,cleaned inspected and rebuilt. The non-leaking side had clean oil in it but the leaking side was like chicken soup. Looks like someone previously only did half a job.......:augie

First fork took me about an hour, second took about 30 minutes.:)
 
Need to do the fork seals on my 520 had a look through the manual,looks pretty straight forward.:D
Also found these videos on youtube is this the best way to do it ?
Don't have a seal driver to sit the seals is there another way to do it ?

Any tips would be appreciated :thumb2


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Cheers Forry :beerjug:
 
KTM's have a bit of a reputation for leaking fork seals especially 06/07 on, a friend of mine thought that the neoprene fork covers/protectors would help keep the dirt & Dust away and so prolong their life.

Anyway, almost everyone I know with a KTM (& husky) now has these, they certainly do seem to do the trick, they also do a shock joint cover that keeps the crud out of the lower shock joint that must help, although to be fair I did change mine and it was goosed.
 
KTM's have a bit of a reputation for leaking fork seals especially 06/07 on, a friend of mine thought that the neoprene fork covers/protectors would help keep the dirt & Dust away and so prolong their life.

Anyway, almost everyone I know with a KTM (& husky) now has these, they certainly do seem to do the trick, they also do a shock joint cover that keeps the crud out of the lower shock joint that must help, although to be fair I did change mine and it was goosed.

My '03 450 EXC hasjust had new forkseals,fittedby my local dealer -£200 all in:eek:

If you leave your bike on its sidestand, the pressure build up is unbelievable. I found that by leaving my bike on a paddock stand ( I think that's what you call them) relieves the pressure on the seals cosiderably.
 
The pressure on the seals is really only there when the forks are being compressed (as the oil is moved from one side of the piston to the other), once the fluid has got where it is going there is no pressure.

There is also a negative pressure created during the rebound phase that could draw in dirt & water through a faulty seal, although the likelyhood of this is much less as you would want to fix it due to oil loss a long time before it bacame a problem.

When they are compressed the weight of the bike is taken by the springs (which can weaken/deform if continuously compressed).

You will note that you can bleed pressure off your forks after they have been used, this is normal, racers bleed it off as it stiffens the forks much like a stronger spring. (you also see forks with schrader valves on that allow air to be pumped in for this reason, I think they are a thing of the past now though)
 
I've never heard so much sh!te in my life, you KTMers make me laugh..... that KTM book of lame excuses again.......:blagblah:D

The seals fail due to two reasons.... they are worn, ie, at the end of service life, or lack of cleaning allows dirt to dry on the slider stanctions, then the next compression takes the dried dirt through the seals, removing the sealing lip.
Worn glacier bushes inside the legs can give the impression that the seals are at fault, but the play in the stanctions is too excessive for the seal to keep the oil contained. Many folk then change the seals but not the bushes and on re-assembly, the seals leak straight away.
I recommend you replace all the bushes with a new seal set. Seal kits are about £12, bush kits about £25. Some outlets do a complete kit for £30. Look in ebay. Job takes about an hour per leg.

Timpo.
 
Timpo,
Check your facts, EXC's have a reputation for leaking fork seals even from new so thats not really related to a worn out fork leg, although I do accept that if you are riding some old nail then it might be fecked.

Very often a pattern seal will resolve it.

I merely made the point that keeping dust & dirt out of the seal will prolong it's life.

Sorry if I offended you- not!
 
Timpo,
Check your facts....

My facts..... I ain't got any.:p Except about the KTM lame excuse book that owners of such bikes use......:D

EXC's have a reputation for leaking fork seals even from new....

Yet the same front legs are fitted to nearly every other brand of euro-enduro, ie, from CCM to TM, from Berg to BMW, from VOR to Benelli.
Like i said, cleaning or lack of it, after the first ride of the bike, will see-off the seals, giving the 'from new' failure.

Sorry if I offended you....

Making me laugh doesn't offend me..... I like laughing.:D

Forry, fetch the legs down, I'll do the job for you..... I've got a seal tool here...... somewhere!:augie

Timpo.
 
Actually the seal never leaked on my KTM

And which particular book of lame excuses are you referring to ???

or is it just a KTM Chip thing :nenau
 
EASY FORK SEAL INSERTION TOOL.

For driving the new seal home, get some plastic pipe of smaller diameter than the fork tube (say roughly an inch and a half/inch and a quarter diameter plumbing pipe) plus a large jubilee (worm-drive) clip. Cut two lengths nice and square, one about 5mm longer than the other. When you have your two plastic tubes cut to length and square, slit them both lengthways.

Fit all components onto the fork leg in the correct sequence then insert the slider into the fork tube.

Fit one plastic 'sleeve' over the other so the outer one sits about 5mm overhanging the inner (on the seal side) and secure tightly to the fork slider with a large jubilee clip.

Use the fork slider with seal tool fitted as a slide hammer to drive the new seal home into its recess then fit the spring circlip into its recess to secure in place. The overhanging lip of the home made tool drives the seal home by its outer edge, the 5mm approx clearance prevents damage to the sealing lip faces. Remove the home made insertion tool before fitting the new outer dust seal. The dust seal can be simply tapped home with a soft rubber faced hammer or similar.

DO NOT SCRIMP AND ONLY FIT THE OIL SEAL - CHANGE BOTH THE OIL SEAL AND DUST SEAL TOGETHER

P.S. I would strongly recommend the aftermarket American brand of "ALL BALLS" fork seal and dust seal kits. Can be got for about £20 + p&p on ebay etc, much better quality than stock. Pay attention that this type of oil seal is the correct way around when fitting, it has several sealing lips and not just one.
 
Timpo is right - the reasons for seal failure are commonly due to dirt.

That said, sometimes the seal can leak - but there is nothing wrong with them - just a trapped grain of sand keeping the seal from... sealing. A swipe with a thin feeler guage can flush the offending grain(s) out and voila youre leaking stops.

There is NO pressure on the seals under normal operation - except for the air-spring effect. The oil damping pressure is inside the cartridge. (in closed cartridge forks like the SXS forks, the damping oil and the lubrication oil are completely independent).

The "common" exc fork seal leakage story is from years ago when KTM used to use single-lipped fork seals. While these provide much lower friction, they dont last as long and are more prone to leaking. I cant remember when exactly they changed - but WP/KTM have been using dual-lipped seals for some time.

Be wary of the aftermarket seals like all-balls - they can often introduce large amounts of static friction - sticky forks tend to feel quite harsh (not my experience, but that of a suspension tuner who has seen 100x more forks/seals than I have)
That said, I have had a brand new set of NOK (WP) seals that were sticky as fook. Had to replace them...
 
My '03 450 EXC hasjust had new forkseals,fittedby my local dealer -£200 all in:eek:

Fark! Did you also get a reach-around for that money?

Not sure what part of the country youre in - but at a proper suspension tuner like On Track Racing - you can get a full service and revalve for about half that.

If you leave your bike on its sidestand, the pressure build up is unbelievable. I found that by leaving my bike on a paddock stand ( I think that's what you call them) relieves the pressure on the seals cosiderably.

Side stand makes no odds - no way for pressure to build up just sitting there.
That said, do make sure you bleed your forks regularly - pressure can build up through usage.
Be wary of the fork bleeder valves - they can stick open - but they are a whole lot more convenient.
 
Hi
Just had my seals done (EXC400 '04) £81.00 new oil, and gen. seals and dust seals. I was riding on Salisbury plain and the front wheel went down an unseen hole at about 50mph. The forks bottomed out so hard I nearly snapped my wrists.Some how I stayed on the bike and the same thing happened to two riders behind me. That made one leg leak oil so new seals were needed. I have fitted some neoprene sock things that cable tie top and bottom and cover the whole stantion ( do they help ? ) :thumb
 
That chalky Salisbury mud is no friend to fork seals.

What typically happens is that you will go through mud which will coat the fork tubes with a thin film. If youre trail riding, youre unlikely to be using the full travel of your suspension, so the film can dry on the tube. That chalk is very fine and dries quite hard.

Then some time later you hit some terrain that really works the full travel of the suspension and that thin layer of dried chalk gets rammed at the fork seal interface. Because its so fine, its probably not completely removed by the dust covers so it ends up either trapping some grit under the oil seal - or abrading it.

IMO fork seal savers (the shorty kind) would help greatly in helping wipe off the dried film. The longer-length ones tend to get 'eaten' by the brake disc.
 
Thanks Mooky
That sounds like the reason. We were on Salisbury plain for 8 hours so chalk mud was everywere. Dry then wet then dry again. I'll see how the long socks go and fit shorty's if they Knacker up......:)
 
Thanks Mooky
That sounds like the reason. We were on Salisbury plain for 8 hours so chalk mud was everywere. Dry then wet then dry again. I'll see how the long socks go and fit shorty's if they Knacker up......:)

If you get a nice, very thick cable tie around the top of the seal saver, the fork guard will rub on that instead of your seal saver - they'll last a lot longer.
 


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